The invention relates to a process for the preparation of a high activity catalyst component for the production of olefin polymers. The invention also relates to a procatalyst prepared by said process and the use of such a procatalyst in the polymerization of olefins.
Olefinic unsaturated monomers such as ethylene can often be polymerized in the presence of a catalyst composition, which has essentially two components: a compound of a transition metal belonging to one of groups 4 to 6 of the Periodic Table of Elements (Hubbard, IUPAC 1990) which is often called a procatalyst, and a compound of a metal belonging to any of groups 1 to 3 of said Table which is often called a cocatalyst. This kind of Ziegler-Natta catalyst composition has been further developed by depositing the procatalyst on a more or less inert and particulate support and by adding to the catalyst composition in the stages of its preparation several additives, among others electron donating compounds. These compounds have improved the polymerization activity of the catalyst, the operating life and other properties of the catalyst composition and first of all properties of the polymers which are obtained by means of the catalyst composition.
When ethylene polymers are produced, the polymer molecules formed are not similar by molecular weight, but a mixture having a narrow or broad molecular weight distribution is developed. The broadness of the molecular weight distribution may be described by utilization of the ratio of two different averages, namely the weight average molecular Mw and the number average molecular weight Mn, where a high value of Mw/Mn indicates a broad molecular distribution. For controlling the molecular weight a so called chain transfer agent can be added to the polymerization reaction mixture. In order to obtain polymer products having different molecular weights, different amounts of the chain transfer agent for controlling the molecular weight must be fed into the polymerization reaction mixture. The most usual and preferable chain transfer agent is hydrogen, because when using it no foreign atoms or atom groups are left in the growing molecule, that would cause inconveniencies for the polymerization process or disadvantageous properties of the polymer produced.
How well the molecular weight of the produced polymer varies as function of the hydrogen amount, i.e. how much the so called hydrogen sensibility changes, greatly depends on the catalyst composition. Generally the problem is, that in polyethylene production the polymerization activity decreases to quite an extent the more hydrogen is present.
This absence of catalyst activity balance is a common drawback for all prior art catalysts today. The imbalance shows up when, using prior art catalysts, a drastic drop in the productivity of the catalysts occurs when going from polymerization conditions giving high molecular weight polymers (low melt flow rate) to polymerization conditions giving low molecular weight polymers (high melt flow rate). Even if such a commercial catalyst can have a quite good productivity at a polymer melt flow rate (MFR, defined according to standard ISO 1133) of 1, there is often only 10% left of the productivity when producing a MFR of 500. Thus it is desirable to provide a catalyst system having a high activity which is independent of the molar mass of the polymer under formation.
The activity balance discussed above is important in production of bimodal polyethylene. There, a low molecular weight component is produced in one stage at a high hydrogen concentration and a high molecular weight component is produced in another stage at a low hydrogen concentration. Since no fresh catalyst is added between these polymerization stages, the catalyst employed in production of bimodal polyethylene must be able to produce the different molecular weights with a high productivity.
EP-A-32307 discloses a procatalyst that has been prepared by treating an inorganic support like silica with a chlorination agent like ethyl aluminium dichloride which support is then contacted with a magnesium alkyl compound like butyl ethyl magnesium, and with titanium tetrachloride (see claim 1, example 1, table 1).
WO-A-96/05236 discloses a catalyst component comprising (i) a particulate support where the majority of particles is in the form of an agglomerate of subparticles and (ii) a magnesium halide. The publication discusses the preparation of the support material. It also describes catalyst preparation and polymerization examples. The catalyst is prepared by adding titanium tetrachloride and DEAC on the agglomerated carrier containing magnesium chloride. The polymerization examples show that a higher bulk density and a higher MFR (better hydrogen response) as well as a lower FRR (narrower molecular weight distribution) is obtaines by the catalyst prepared according to the disclosure. The publication does no refer to the homogeneity of the material.
EP-A-688 794 discloses a process for the preparation of a high activity procatalyst, wherein an inorganic support is reacted with an alkyl metal chloride, the first reaction product is reacted with a compound containing hydrocarbyl and hydrocarbyl oxide linked to magnesium, and the obtained second reaction product is contacted with a titanium chloride compound. The obtained procatalyst has good activity both at high and low MFR polymerization conditions, but it has the drawback of giving an inhomogeneous ethylene polymer product, resulting in gels and white spots in the polymer material. These inhomogenities have detrimental effect on the appearance and mechanical properties of polyethylene film.
The drawbacks encountered by EP-A-688 794 and other prior art catalysts have now been eliminated by a modified process, characterized by the steps of reacting a support, at least the surface of which comprises a magnesium halide compound having the formula (1):
(RO)2xe2x88x92nMgXnxe2x80x83xe2x80x83(1)
wherein R is a C1-C20 alkyl or a C7-C26 aralkyl, each same or different X is a halogen, and n is an integer 1 or 2,
an alkyl metal halide compound having the formula (2):
R1n1Mm1X1(3m1xe2x88x92n1)xe2x80x83xe2x80x83(2)
xe2x80x83wherein M is B or Al, each same or different R1 is a C1-C10 alkyl, each same or different X1 is a halogen, n1 is 1 or 2 when m1 is 1 and n1 is an integer from 1 to 5 when m1 is 2,
a magnesium composition containing magnesium bonded to a hydrocarbyl and magnesium bonded to a hydrocarbyl oxide, said magnesium composition having the empirical formula (3):
R2n2(R3O)2xe2x88x92n2Mgxe2x80x83xe2x80x83(3)
xe2x80x83wherein each same or different R2 is a C1-C20 alkyl, each same or different R3 is a C1-C20 alkyl or a C1-C20 alkyl containing a hetero element, and n2 is between 0.01 and 1.99, and
a titanium halide compound having the formula (4):
(R4O)n3TiX24xe2x88x92n3xe2x80x83xe2x80x83(4)
xe2x80x83wherein each same or different R4 is a C1-C20 alkyl, each same or different X2 is a halogen, n3 is 0 or an integer 1-3, and Ti is quadrivalent titanium.
By the formula (1) is meant that the inorganic support may be coated by MgCl2 or RoMgCl. Thus n is 1 or 2.
By xe2x80x9cmagnesium compositionxe2x80x9d above is meant a mixture or a compound. Note that formula (3) is an empirical formula and expresses the molar amounts of alkyl R2 and alkoxy OR3 relative to the amount of magnesium Mg, which has been defined as 1, and differs from formulas (1), (2) and (4), which disclose the molecular composition of distinct compounds only.
A procatalyst has now been discovered by which ethylene homopolymers or copolymers having low or high molecular weights can be produced with an even and high activity as well as a homogeneous consistance. Independently of the amount of hydrogen introduced into the polymerization reactor, the activity of the catalyst remains more or less unchanged and a homogeneous ethylene polymer product is obtained.
The unique feature of the catalyst according to the invention now lies over its good balance in activity and a homogeneous product in a very wide range of molar mass regulating hydrogen partial pressures used in the polymerization. It is thus possible to carry out an ethylene polymerization by the use of this catalyst at high and low melt flow and still have very similar high productivity as well as a homogeneous, gel free product. This MFR/activity balance renders the catalyst universally applicable for most types of PE resins in all polymerization processes using heterogeneous catalyst systems.
Preferably, the claimed process comprises the subsequent steps of:
a) providing said support comprising a magnesium halide compound having the formula (1),
b) contacting said support comprising a magnesium halide compound having the formula (1) with said alkyl metal halide compound having the formula (2), to give a first product,
c) contacting said first product with said magnesium composition containing magnesium bonded to a hydrocarbyl and magnesium bonded to a hydrocarbyl oxide and having the empirical formula (3), to give a second product, and
d) contacting said second product with said titanium halide compound having the formula (4).
The support used in the process is preferably in the form of particles, the size of which is from about 1 xcexcm to about 1000 xcexcm, preferably about 10 xcexcm to about 100 xcexcm. The support material must have a suitable particle size distribution, a high porosity and a large specific surface area. A good result is achieved if the support material has a specific surface area between 100 and 500 m2/g support and a pore volume of 1-3 ml/g support.
The above catalyst components (2) to (4) are reacted with a suitable catalyst support. If the catalyst components (2) to (4) are in the form of a solution of low viscosity, a good catalyst morphology and therewith a good polymer morphology can be achieved.
It is advantageous if in the magnesium halide compound having the formula (1), R is a C1-C20 alkoxy or a C7-C26 aralkoxy. However, it is preferable, if said compound (1) is a magnesium dihalide, most preferably MgCl2. For example, the support may comprise solid MgCl2, either alone as a powder, or as a powder mixture with other inorganic powders.
According to another embodiment of the invention, the support comprising a magnesium halide compound having the formula (1) also comprises an inorganic oxide. Several oxides are suitable, but silicon, aluminium, titanium, chromium and zirconium oxide or mixtures thereof are preferred. The most preferred inorganic oxides are silica, alumina, silica-alumina, magnesia and mixtures thereof, uttermost preferably silica. The inorganic oxide can also be chemically pretreated, e.g. by silylation or by treatment with aluminium alkyls.
It is recommendable to dry the inorganic oxide before impregnating it by other catalyst components. A good result is achieved if the oxide is heat-treated at 100xc2x0 C. to 900xc2x0 C. for a sufficient time, and thereby the surface hydroxyl groups, in the case of silica, are reduced to below 2 mmol/g SiO2.
According to this aspect of the invention, the support comprises particles having a core comprising said inorganic oxide and a shell comprising said magnesium halide compound having the formula (1). Then, the support comprising a magnesium halide compound having the formula (1) and an inorganic oxide can conveniently be prepared by treating particles of the inorganic oxide with a solution of the magnesium halide and removing the solvent by evaporation.
When using a support containing both said magnesium halide compound (1) and another component, the amount of magnesium halide compound (1) is such that the support contains from 1 to 20% by weight, preferably from 2 to 6% by weight, of magnesium.
The invention further comprises a step of reacting an alkyl metal halide compound of the formula (2):
R1n1Mm1X1(3m1xe2x88x92n1)xe2x80x83xe2x80x83(2)
wherein M is B or Al, each same or different R1 is a C1-C10 alkyl, each same or different X1 is a halogen, m1 is 1 or 2, n1 is 1 or 2 when m1 is 1 and n1 is an integer from 1 to 5 when m1 is 2. In formula (2), M is preferably Al. Each same or different R1 is preferably a C1-C6 alkyl, and, independently, the preferred same or different halogen X1 is chlorine. n1 is preferably 1 and m1 is preferably the integer 1 or 2. Most preferably, the alkyl metal halide compound having the formula (2) is an alkyl aluminium dichloride, e.g. ethyl aluminium dichloride (EADC).
The alkyl metal halide compound is preferably deposited on the support material. An even deposition is preferably achieved if the viscosity of the halide or its solution is below 10 mPa*s at the temperature applied. To achieve this low viscosity the alkyl metal halide can be diluted by a non-polar hydrocarbon. The best deposition is however achieved if the total volume of the absorbed alkyl metal halide solution is not exceeding the pore volume of the support. A good choice is to use a 5-25% hydrocarbon solution of ethyl aluminium dichloride. The number of additions of the halide is preferably adjusted so that the technique are of not exceeding the pore volume at any additions is not violated, thereby giving an even distribution of the chemical in the surface of the support material.
In the above mentioned preferred order of reaction steps a) to d), step b) can advantageously be performed so that undiluted alkyl metal halide (2) is used to treat the support comprising a magnesium halide compound having the formula (1). Alternatively, the support is contacted with a solution of the alkyl metal halide compound having the formula (2) in an essentially non-polar solvent, preferably a non-polar hydrocarbon solvent, most preferably a C4-C10 hydrocarbon. The concentration of the alkyl metal halide compound having the formula (2) in said non-polar solvent is usually 1-80% by weight, preferably 5-40% by weight, most preferably 10-30% by weight. Advantageously, the support is contacted with a solution of said alkyl metal halide compound (2) in a ratio mol of the alkyl metal halide compound (2) to grams of the support of between about 0.01 mmol/g and about 100 mmol/g, preferably between about 0.5 mmol/g and about 2.0 mmol/g. The amount of reactants can also be expressed as molar ratio, whereby it is advantageous, if the molar ratio of said alkyl metal halide compound (2) to said magnesium halide compound (1) of the support is between about 0.01 mol/mol to about 100, preferably about 0.1 mol/mol to about 10, most preferably from about 0.2 to about 3.0.
In step b), the temperature at said contacting is e.g. 5-80xc2x0 C., preferably 10-50xc2x0 C., most preferably 20-40xc2x0 C. The duration of said contacting is 0.1-3 h, preferably 0.5-1.5 h.
In the claimed process, the magnesium composition containing magnesium bonded to a hydrocarbyl and magnesium bonded to a hydrocarbyl oxide and having the empirical formula (3), each same or different R2 is preferably a C2-C10 alkyl, most preferably a C2-C8 alkyl. Each same or different R3 is preferably a C3-C20 alkyl, more preferably a branched C4-C10 alkyl, most preferably a 2-ethyl-1-hexyl or a 2-propyl-1-pentyl.
The magnesium composition containing magnesium bonded to a hydrocarbyl and magnesium bonded to a hydrocarbyl oxide having the empirical formula (3) can also be defined by its preparation. According to one embodiment of the invention, it is a contact product of a dialkyl magnesium having the formula (5):
R22Mgxe2x80x83xe2x80x83(5)
wherein each same or different R2 is defined as above, and an alcohol. Preferably, the dialkyl magnesium having the formula (5) is dibutyl magnesium, butyl ethyl magnesium or butyl octyl magnesium.
The magnesium composition can thus be defined in that the magnesium composition containing magnesium bonded to a hydrocarbyl and magnesium bonded to a hydrocarbyl oxide having the empirical formula (3) is a contact product of a dialkyl magnesium and an alcohol having the formula (6):
R3OHxe2x80x83xe2x80x83(6)
wherein each same or different R3 is the same as above. Preferably, the alcohol having the formula (6) is a 2-alkyl alkanol, most preferably 2-ethyl hexanol or 2-propyl pentanol. It has been found that such branched alcohols give better results than linear alcohols.
Preferably, the magnesium composition containing magnesium bonded to a hydrocarbyl and magnesium bonded to a hydrocarbyl oxide having the empirical formula (3) is a contact product of a dialkyl magnesium and an alcohol in a molar ratio alcohol to dialkyl magnesium of 0.01-100 mol/mol, preferably 1.0-5.0 mol/mol, more preferably 1.7-2.0 mol/mol, most preferably 1.8-1.98 mol/mol. The dialkyl magnesium and the alcohol are conveniently contacted by adding the alcohol to a solution of said dialkyl magnesium in an organic solvent, e.g. a C4-C10 hydrocarbon. Then, the concentration of the solution is preferably between 1 and 50% by weight, most preferably between 10 and 30% by weight. The contacting temperature between the dialkyl magnesium and the alcohol is preferably 10-50xc2x0 C., more preferably from about 20xc2x0 C. to about 35xc2x0 C.
In step c) of the above mentioned preferred order a)xe2x86x92d) of the claimed process, the contacting product of the support with the alkyl metal halide compound (2) (=said first product) is contacted with said magnesium composition containing magnesium bonded to a hydrocarbyl and magnesium bonded to a hydrocarbyl oxide and having the empirical formula (3).
Preferably, said first product is contacted with said magnesium composition (3) in a ratio moles of magnesium/g of the support of between 0.001-1000 mmol/g, preferably 0.01-100 mmol/g, most preferably 0.1-10 mmol/g (g of the support means, in the case of said first reaction product, the support which was used as starting material for the first reaction product).
A good deposition of said magnesium composition as a solution is achieved if the volume of the magnesium composition (3) solution is about two times the pore volume of the support material. This is achieved if the concentration of the composition in a hydrocarbon solvent is between 5-60% in respect of the hydrocarbon used. When depositing the magnesium composition on the support material its hydrocarbon solution should have a viscosity that is lower than 10 mPa*s at the temperature applied. The viscosity of the magnesium complex solution can be adjusted for example by the choice of the group R4 in the formula (3), by the choice of the concentration of the hydrocarbon solution, by the choice of the ratio between the magnesium alkyl and the alcohol or by using some viscosity lowering agent. The titanium compound can be added to the support material with or without a previous drying of the catalyst to remove the volatile hydrocarbons. Remaining hydrocarbons can if desired be removed by using slight underpressure, elevated temperature or nitrogen flash.
In the claimed process, the transition metal compound is a titanium halide compound having the formula (4). R4 is preferably a C2-C8 alkyl, most preferably a C2-C6 alkyl. X2 is preferably chlorine and, independently, n3 is preferably 0. Said titanium halide compound having the formula (4) is advantageously titanium tetrachloride.
According to one embodiment of the invention, in addition to said titanium compound having the formula (4), a titanium compound having the formula (7):
(R5O)n4TiX34xe2x88x92n4xe2x80x83xe2x80x83(7)
wherein each same or different R5 is a C1-C20 alkyl, preferably a C2-C8 alkyl, most preferably a C2-C6 alkyl, each same or different X3 is a halogen, preferably chlorine, n4 is an integer 1-4, and Ti is quadrivalent titanium, is reacted. The titanium compound (7) always has at least one alkoxy group, which helps dissolving the titanium compound (4) which does not necessarily contain alkoxide, into an organic solvent before the contacting. Naturally, the more alkoxide groups compound (4) has, the less is the need for compound (7). If compound (7) is used, the preferable combination is that of titanium tetrachloride and a titanium tetra C1-C6-alkoxide.
In step d) of the preferred step sequence a)xe2x86x92d), said second product is advantageously contacted with the titanium compound having the formula (4) in a ratio moles of said titanium compound/g of the support of 0.01-10 mmol/g, preferably 0.1-2 mmol/g. Preferably, said second reaction product is contacted with said titanium compound (4) in a ratio moles of said titanium compound (4)/moles of the magnesium compound (3) of 0.05-2 mol/mol, preferably 0.1-1.2 mol/mol, most preferably 0.2-0.7 mol/mol. The temperature is usually 10-80xc2x0 C., preferably 30-60xc2x0 C., most preferably from about 40xc2x0 C. to about 50xc2x0 C., and the contacting time is usually 0.5-10 h, preferably 2-8 h, most preferably from about 3.5 h to about 6.5 h.
Above, the process for the preparation of a high activity catalyst component for the production of olefin polymers of different molecular weight and homogeneous consistence, has been described in detail. The invention also relates to such a high activity catalyst component. The suitability for both low and high molecular weight polymerization means, that the claimed catalyst component has high activity both when producing low melt flow rate ethylene polymer and high melt flow rate polymer. High molecular weight polymer has high melt viscosity, i.e. low melt flow rate, and low molecular weight polymer has low melt viscosity, i.e. high melt flow rate.
Simultaneously or separately, it preferably produces ethylene homopolymer and copolymer with low gel content. Most preferably it produces ethylene homopolymer having a Gel number, measured under specified test conditions, of approximatively 0/0 l/m2. This means, that by the standards used, the claimed catalyst components can be used to produce totally homogenous (gelless) low and high molecular weight ethylene polymer.
The invention also relates to the use of a catalyst component according to the invention in the polymerization of olefins, preferably in the homo- or copolymerization of ethylene. The advantage of the use is based on the fact that the claimed catalyst is suitable for both low molecular weight and high molecular weight ethylene polymerization and that the ethylene polymer produced is of high quality.
In the polymerization, said alkyl metal halide compound of the formula (2) can, if used, also act completely or partially as a cocatalyst. However, it is preferable to add a cocatalyst having the formula (9):
R6n5AlX43xe2x88x92n5xe2x80x83xe2x80x83(9)
wherein R6 is a C1-C20 alkyl, preferably a C1-C10 alkyl, most preferably a C2-C6 alkyl such as ethyl, X is a halogen, preferably chlorine, n is 1 to 3, more preferably 2 or 3, most preferably 3, to the polymerization mixture. The cocatalyst having the formula (9) is optional depending on whether said alkyl metal halide compound (2) is acting as cocatalyst or not.
Those familiar with the art know that the gel level is influenced by two properties of the polymer, the average molecular weight (for which the melt flow rate, or MFR, is an often used measure) and the broadness of the molecular weight distribution (for which the shear thinning index, or SHI, and the flow rate ratio, or FRR, are often used measures). A high molecular weight (or, a low MFR) usually results in a higher gel level than a low molecular weight (or, a high MFR). Also, a broad molecular weight distribution (or, a high SHI or FRR) usually results in a higher gel level than a narrow molecular weight distribution (or, a low SHI).
Pelletized material samples were blown to a film on a pilot film line. The film blowing conditions were:
Die diameter 30 mm
Die gap 0.75 mm
Blow-up ratio 3.0
A sample of the size 210 mmxc3x97297 mm was cut from a film blown on the Collin line. The film sample was put into a gel scanner, which classifies the gels according to their size. The scanner gives the number of gels in three size classes,  less than 0.3 mm, 0.3 . . . 0.7 mm and  greater than 0.7 mm. Generally the number of gels in the smallest class can be affected by different random factors, so often only the numbers of the intermediate (0.3 . . . 0.7 mm) and large ( greater than 0.7 mm) gels are given.
The dispersion indicates the homogeneity of the black samples in a similar fashion as the gel level indicates the homogeneity of the film samples. It is measured from the black pellets according to the ISO/DIS 11420 method as follows:
Six pellets are cut using a microtome to 20 xcexcm cuts. Using an optical microscope, the white spots seen in the sample are then measured and classified according to their size. The average number of white spots in each size class is calculated. An ISO value indicating the dispersion is attributed to the material. A high ISO rating denotes a poor homogeneity (large inhomogeneities).